The present invention relates to automatic gain control in a receiver.
Incoming signals in a wireless communication receiver can vary widely in signal strength due to a variety of factors such as distance from the transmitter, obstacles in the propagation path, interference from other signals, etc. The signal strength variations can diminish receiver operation quality. Hence, many wireless receivers employ an automatic gain control (AGC) technique to maintain incoming signal levels within a receiver's optimal operational range.
In some conventional AGC systems, a feedback path is used to control gain blocks at a front-end of the receiver. The front-end includes analog gain blocks that operate in the radio frequency (RF) band. Typically, front-end gain is maximized to obtain the lowest possible noise figure, which leads to a high signal-to-noise ratio (SNR). Out-of-band signals, however, can significantly degrade receiver performance. Out-of-band signals can drive the front-end gain blocks into an overload condition where their linearity suffers because of the front-end's larger bandwidth of operation. As a result, out-of-band signals can force the AGC to reduce the gain unnecessarily, leading to SNR degradation.
In some other conventional AGC systems, only baseband gain blocks are controlled by the AGC. Baseband blocks follow mixer(s) that down convert the RF signal to a baseband frequency. Lone baseband gain control cannot fully account for large variations in the signal strengths because of the narrow bandwidth of baseband gain blocks. Therefore, both front-end-only and baseband-only AGC systems have severe drawbacks. Even if some conventional AGC systems control both front-end and baseband gain blocks, the gain reduction mechanisms are generally static and follow a predetermined fixed profile.
Hence, the inventors perceive a need in the art for a dynamic AGC system that can control both front-end gain blocks and baseband gain blocks to optimize receiver operations.